1. Field of the Invention
The present invention relates to a hot runner injection molding machine equipped with heaters for heating an injection molding compound in an injection passage, to keep the compound in a molten condition.
2. Description of the Related Art
An injection molding machine equipped with heaters for heating an injection passage (hereinafter called "runner") for a melted injection molding compound (hereinafter called "a melt") to be injected into the cavity is commonly used for manufacturing plastic products.
In this type of injection molding machine, usually a runner is disposed within a front mold, and heaters for heating the runner are also installed within the front mold. By this arrangement, the melt in the runner can be maintained in a melted condition even when the melt is injected into the cavity.
This type of injection molding machine is disclosed, for example, in Japanese Examined Patent Publication No. 61-59219.
In this type of injection molding machine, however, each front mold is equipped with its own built-in heaters and runners, and therefore, the cost of manufacturing the front mold becomes higher.
Japanese Unexamined Patent Publication No. 63-202418 discloses another type of injection molding machine, in which a runner device having a passage for a melt is provided separately and fixed to a fixed head of the injection molding machine.
This arrangement allows a single runner device to be utilized for different front molds, and thus the cost of manufacturing the front mold can be reduced.
Even in this case, however, it is difficult to change the nozzle (or gate) without removing the runner device.
Consequently, when it is necessary to change the length of the nozzle (or gate) in accordance with the type of front mold, the runner device must be removed, or the whole runner device including the nozzle (or gate) must be changed.